The present invention relates to water purification and more particularly to the removal of dissolved minerals and carbonates from water in order to diminish its so-called "hardness".
The overwhelming majority of water in the United States is "hard". Elsewhere, this proportion may vary, but hard water is found in many, if not most regions of the world. Where it is found, it creates serious difficulties. Not only does it cause scale to form inside the pipes, storage vessels, and the like in which the water is contained, but it causes problems even after passage through these containers. For example, hard-water makes it necessary to use excessive quantities of water softeners and/or soap or detergent when the water is used for washing, and it also leaves calcium-type deposits analogous to scale in or on the articles washed with that water. As another example, hard water dissolves some substances less readily than water whose hardness has been reduced, or eliminated.
The substances which cause hardness in water normally are present in the form of dissolved ions, predominantly calcium and bicarbonate ions. Due to their extremely small size (of the order of 10.sup.-10 microns), these dissolved ions cannot be readily filtered out of the water using conventional and relatively inexpensive water filters. Rather, more exotic removal techniques have had to be used, such as reverse osmosis or ion exchanger. Those techniques are too expensive for use in other than specialized applications. For example, for domestic usage, the multi-hundred dollar cost of a reverse osmosis installation tends to be regarded as prohibitive by most prospective users, and this problem would be compounded by the need to professionally service the installation, also at substantial recurrent cost for maintenance.
Alternatively, chemicals could be added to the "hard" water to soften it. However, these chemicals, in turn, have residues which have their own undesirable characteristics. For example, adding sodium chloride (used in conventional water softeners) leaves behind, in the (softened) water, the sodium portion, with its well-known undesirable side effects.